Field of the Invention
The present invention relates to a spectral apparatus, a detection apparatus, a light source apparatus, a reaction apparatus, and a measurement apparatus.
Description of the Related Art
The performance of a spectral apparatus is represented by the magnitude of a wavelength resolution (λ/Δλ). In particular, a high-resolution spectral apparatus is required to have a resolution more than 100,000. The theoretical critical resolution of a spectral apparatus using a diffraction element (diffraction grating) is uniquely determined depending on how much optical path difference can be ensured between the light components of respective wavelengths. Hence, to implement a high resolution in a spectral apparatus, a large diffraction element is necessary. For example, along with the progress of a high-repetition rate femtosecond laser or a high-output titanium sapphire femtosecond laser, a highly efficient transmissive type diffraction element as large as 150 mm or more is available nowadays. However, the actual resolution of the spectral apparatus is also limited by the incident size, imaging magnification, and optical aberrations of the spectral apparatus, and the resolution of a detector. In addition, when the diffraction element is made large, aberrations readily occur. It is therefore difficult to implement a high resolution by simply upsizing the diffraction element. Technologies associated with such a spectral apparatus have been proposed in Japanese Patent Laid-Open Nos. 2009-121986, 2006-162509, 1-292221, 2011-257140, and 59-165017.
On the other hand, an optical comb light source that outputs a train of optical pulses at temporally equal intervals has received attention in recent years. These pulses have a high phase relationship and interfere with each other. For this reason, the spectrum has a comb-shaped structure in which light components exactly apart by a predetermined frequency are arrayed at equal intervals. Such a comb-shaped spectral structure is generally called a longitudinal mode. Since the wavelengths of the longitudinal modes are slightly different, a spectral apparatus is used to spatially separate the longitudinal modes.
However, to actually separate the longitudinal modes, a spectral apparatus having a very high resolution is necessary. In addition, it is very difficult to implement a spectral apparatus capable of making a separated longitudinal mode usable as a light source. For example, the longitudinal mode interval of a generally available optical comb light source corresponds to an optical frequency of about 1 GHz. To separate the longitudinal modes of the optical comb light source, a spectral apparatus having a resolution more than at least 300,000 is necessary because the optical frequency is 300 THz. To implement such a resolution, the spectral apparatus needs to be constructed using a reflective type diffraction element larger than 300 mm, resulting in a bulky spectral apparatus.
If the longitudinal modes can be separated (extracted), a continuous wave light source or a light source capable of generating light of an arbitrary waveform can be implemented. Hence, the absolute efficiency (the ratio of input (amount of incident light) to the spectral apparatus to output (amount of light spectrally separated at a predetermined resolution)) of the spectral apparatus is very important. For the conventional spectral apparatus, however, improving the signal-to-noise ratio has priority in general from the viewpoint of detection accuracy. The absolute value of the output is rarely considered important, and techniques (arrangement and the like) for improving the absolute efficiently of the spectral apparatus are lesser known.